In the related art, there are known observation apparatuses that are provided with a high-sensitivity photodetector, such as a photomultiplier tube (hereinafter, referred to simply as a “PMT”) or an EM-CCD, and that prevent deterioration of or damage to the photodetector caused by the entry of excessive light thereto (for example, see Patent Literatures 1 and 2).
With a microscope described in Patent Literature 1, it is judged whether or not light intensity signals exceeding a predetermined threshold have been output from a photodetector over a plurality of continuous pixels, and the HV (High Voltage) to be applied to the photodetector is set to zero if it is judged that there has been such an output. In addition, with an observation apparatus described in Patent Literature 2, a sensor detects the open state of a lid of a black box that accommodates a detector or the like, and the entry of light to the photodetector is blocked by a shutter if it is detected that the lid is in the open state.